Energy Changes PDF | PDF - Free Printable

Problem Description:

The provided document explains the concepts of energy changes during chemical reactions, specifically focusing on bond-breaking and bond-making processes. It also discusses how to determine whether a reaction is exothermic or endothermic using energy diagrams. The task likely involves applying these concepts to analyze a given chemical reaction or interpret an energy diagram.

Since no specific problem is stated in the image, I will create a hypothetical problem based on the content and solve it step by step.

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Hypothetical Problem:

Consider the following chemical reaction:
\[
\text{A} + \text{B} \rightarrow \text{C}
\]
The energy required to break the bonds in reactants \( \text{A} \) and \( \text{B} \) is \( 150 \, \text{kJ} \). The energy released when new bonds form in product \( \text{C} \) is \( 200 \, \text{kJ} \).

1. Determine whether the reaction is exothermic or endothermic.
2. Calculate the enthalpy change (\( \Delta H \)) for the reaction.
3. Sketch an energy diagram for this reaction.

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Solution:

#### Step 1: Understand the Concepts
- Bond-breaking: Energy is absorbed (endothermic process).
- Bond-making: Energy is released (exothermic process).
- Exothermic Reaction: More energy is released during bond-making than is absorbed during bond-breaking. \( \Delta H < 0 \).
- Endothermic Reaction: More energy is absorbed during bond-breaking than is released during bond-making. \( \Delta H > 0 \).

#### Step 2: Analyze the Given Data
- Energy absorbed to break bonds in reactants \( \text{A} \) and \( \text{B} \): \( 150 \, \text{kJ} \).
- Energy released when new bonds form in product \( \text{C} \): \( 200 \, \text{kJ} \).

#### Step 3: Calculate the Enthalpy Change (\( \Delta H \))
The enthalpy change (\( \Delta H \)) for the reaction is given by:
\[
\Delta H = \text{(Energy absorbed in bond-breaking)} - \text{(Energy released in bond-making)}
\]
Substitute the given values:
\[
\Delta H = 150 \, \text{kJ} - 200 \, \text{kJ} = -50 \, \text{kJ}
\]

#### Step 4: Determine Whether the Reaction is Exothermic or Endothermic
- Since \( \Delta H = -50 \, \text{kJ} \), the reaction releases more energy than it absorbs.
- Therefore, the reaction is exothermic.

#### Step 5: Sketch the Energy Diagram
For an exothermic reaction:
- The energy of the reactants is higher than the energy of the products.
- The difference between the energy of the reactants and the products represents the enthalpy change (\( \Delta H \)).

Here is a description of the energy diagram:
1. Draw a horizontal axis labeled "Progress of reaction."
2. Draw a vertical axis labeled "Energy."
3. Place the energy level of the reactants (\( \text{A} + \text{B} \)) at a higher position on the energy axis.
4. Place the energy level of the products (\( \text{C} \)) at a lower position on the energy axis.
5. Indicate the energy released during the reaction as a downward arrow from the reactants to the products.
6. Label the enthalpy change (\( \Delta H = -50 \, \text{kJ} \)) on the diagram.

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Final Answer:

1. The reaction is exothermic.
2. The enthalpy change (\( \Delta H \)) is \( \boxed{-50 \, \text{kJ}} \).
3. The energy diagram shows the reactants at a higher energy level than the products, with an energy release of \( 50 \, \text{kJ} \).

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